Method of making metallic inlaid friction surfaces



Nov. 15, 1938. c. BocKlUs'ET AL. 2,135,370

METHOD OF MAKING METALLIC INLAID FRICTION SURFACES Original Filed Jan. 25, 193'? 2 Sheets-Sheet l NOV. 15, 1938. C, BQCKlUs Er AL, 2,136,370

METHOD OF MAKING METALLIC INLAID FRICTION SURFACES Original Filed Jan. 23, 1937 2 Sheets-Sheet 2 o or/zey Patented Nov. l5, 1938 UNITED STATES PATENT oFFicE METHOD F MAKING METALLIC INLAID FRICTION SURFACES of New Jersey Original application January 23, 1937, Serial No. 121,930. Divided and this application May 17, v 1937, Serial No. 143,104

` Claims.

This application is a division of our co-pending application Serial No. 121,930 filed January 23, 1937.

This invention refers specifically to a process of making friction material wherein metal inlays derived from powdered metal are incorporated in the body of the friction element.

It is well recognized that the presence of cer- `tain typesv ofr `metals or'alloys at the engaging surface of a friction material during engagement imparts a, desired frictional quality. At relatively low engaging temperatures low melting point metals function in a desirable manner. However, at relatively high engaging temperatures, the low melting point metals liquefy'dand are lost.

To 'obtainthe advantages of metals atrelative ly high engaging temperatures, it has heretofore been proposed to incorporate `relatively high melting point metals in the friction material, 0 either alone, in the form of alloys or with metals of lower melting point. However, due to the manner of incorporating such metals, the metals have functioned individually and with little or no cooperative effect. That is, at low engaging temperatures, if low `melting point and high melting point metals are used, the lowl melting point metal will plasticize andev'entually'liquefy. During this period'the high melting point metal will not be appreciably changed nor will it impart any useful function, in fact, it may cause scoring. If andwhen the engaging temperature reaches the melting point or the point where appreciable plasticity of the higher melting point metal occurs, the lower melting' point metal will have long since liquefiedand the available supply Fix thereof will have been lost. However,` in kmost cases the engaging temperature never raises to the point where appreciable benefit may be ob' tained from the higher melting point metal.

This indifferent and unsatisfactorycondition,

association of the metan inthe friction material.

For instance, one wel? known practicel consists 'in` homogeneously mixing metal powders of differ# L5 enttype metals with the friction material. kAlthough some beneficial results have been obtained, at lower engaging temperatures, little or no benefit has been obtained from the higherv melting point metals either at high or low en-` ,0 gaging temperatures. Again, metal wires ofxdiffl ferent physical characteristics have .been used@ with substantially the same effect. Metal inserts `have alsoY been proposed comprising blocks or "buttons of metal, the metal inserts of different ,5 characteristics being spaced from each other by we Vhave found, is primarily due to the improper material.

the base material of the friction element. Here, again, indifferent success has been obtained.

We have found that if relatively soft metals of comparatively low melting point are properly associated with ductlle metals of relatively high melting point, the first mentioned metal, in some manner, iniiuences the properties of the higher melting point metal so that a, metallic lm is secured by which desirable frictional engagement is obtained at an extremely wide range of engagement temperatures. In addition, the higher melting point metal will not tend to produce scoring at low engagement temperature, nor will the supply of klow melting point metal be materially depleted or lost at high engagement temperatures.

Brieiiy described, our invention contemplates the incorporation of the powder of two or more metals ofv different physical properties into a friction material, the metal powders forming, when the friction material is finished, inlays each composed of said metals. The metals comprise at least one soft metal of relatively low melting point and at least one ductile metal of relatively high `melting point. 'I'he softer metal thus brought into intimate relationship with the ductile metal of higher melting point appears to act upon (either chemically or physically) the higher melting point metal and so modify the characteristics of the latter as to form a iilm which is unattainable with either of the metals alone or with both metals not associated in the manner described.

Broadly our invention contemplates a friction material carrying such metals in intimate association irrespective of the manner of application of the metals to the base material or the state of the metal during application. Another aspect of the invention resides in the application of the metals to the friction base materialin powdered form resulting in inlays in the finished friction Other .objects and advantages of our invention will be apparent from the accompanying drawings and following detailed description.

In the drawings, Fig. l is a fragmentary face view of a friction material provided with pow-- Fig. 5 is a sectional view through the element shown in Fig. 4 before compression.

Fis. 6 is a sectional view taken on line I-O 0f F18. 4. I

Fig. 7 is a fragmentary face view of a friction material illustrating another modincation of our invention.

Fig. 8 is a sectional view thereof before compression or cure.

Fig. 9 is a sectional view taken on line 8-l of Fig. 7.

Fig. 10 is a cross-sectionalview of a portion of a spirally wound clutch facing carrying powdered metal between the convolutions of the4 spiral adjacent the working face of the facing.

Fig. l1 is a fragmentary face view of the facing after compression and cure.

Fis. 12 is a sectional view taken on line I2-I2 of Fig. 11.

Fig. 13 is a perspective view of a spirally wound clutch facing carrying a powdered metal inlay between the convolutions adjacent the working face of the facing.

Referring in detail to the drawings. I indicates a fragmentary portion of a friction element such, for example, as used for clutch facings or brake linings. The element I is illustrated as an unwoven friction material such-as a molded, sheeted or extruded material comprising essentially asbestos and a binder, preferably a heat hardenable binder. However, as will be apparent hereinafter, our invention is equally applicable to woven friction elements as well as to those oi' the unwoven type.

During or after the formation of the element I, and before compression and cure, recesses 2 are provided in one face of the element, preferably opening to the working face of the element. The recesses may be of any desired shape and A any desired number thereof may be provided in a predetermined area of the face of the element. The recesses are provided to a depth suiliciently below the surface of the element to provide adequate anchorage for the metal inlays hereinafter described.

Prior to compression and cure as illustrated in Fig. tioned in each of the recesses 2. After compression and cure, as illustrated in Figs. 1 and 3, the element I is reduced in thickness and the powdered metal I appears as metal inlays 4, the

s surfaces of which are adjacent to. or flush with the surface of the element. Of course, during or after the compression step the element is heat treated to cure the binder and under some circumstances the element is baked at a temperature as high as 550 F.` However, it is not necessary to heat treat or sinter the metal inlays in any way other than the heat required to cure and bake the element. It is possible to heat treat or bake the element up to 800 F., the approximate breakdown point of asbestos. In cases where the mechanical interlock between the inlays 4 and friction element base offers poor support and crumbling of the inlay might occur,-

the higher temperature treatment has advantages. However, in general practice, it is usually unnecessary to employ heat other than required to cure and bake the element.

'I'he composition of the metal powder inlay may Vary considerably but preferably comprises at least a soft metal of relatively low melting point and a relatively ductile metal of comparatively high melting point. Metals which have been found exceptionally suitable are copper,

of the element, 2, powdered metal 3 is posilead. tin, zinc, aluminum and soft iron. It is to be understood that these metals may be used in any desired mixture or alloys of some of said metals may be used with other metals or alloys of other of said metals. When the metals comprising the inlays 4 contact the opposing member (the brake drum or clutch pressure plate, in the case of a brake lining or clutch facing), the metals smear and form a relatively light or thin film, possibly mixed with some of the binder compound which is abraded from the body of the element, over substantially the entire surface oi' said opposing member. 'I'he metallic nlm so formed may or may not alloy, depending upon the metals and the working temperature of the surface.

As has been hereinbefore described, it is preferable that metals or alloys be chosen on the basis 'of their relative ductility and melting point. and that a mixture is preferably employed comprising asoft metal of relatively low melting point and a relatively ductile metal of comparstively high melting point. For example, we have found that solder (an alloy of lead and tin) and copper form a desirable .film on the working faces. It appears that the solder, the soft metal of low melting point, acts to assist the copper to form a composite nlm having desired properties which nlm would not be formed by the solder or copper acting alone or being present in the friction base in a less intimate relationship.

When solder and copper are employed the inlay may comprise about forty to seventy-percent y copper, ten to fifty percent lead and naught to thirty percent tin. Undoubtedly some alloying of the copper and tin occurs in operation, that is. at the working face. but whether this is soA or not, the desirable results are obtained. The properties of the above mixturegor combination may be changed by changing. thegproportion of the metals or by adding additional.. metals. 0f course, this example is not to be construed as a limitation since various other mixtures, combinations or alloys may be employed.

The presencefof the soft metal of relatively low melting point, of course, imparts desirable frictional qualitiesmarticularly at low temperatures. 'I'he presence of the ductile metal of higher melting point gives the fllm a degree of stability against heat and acts as a seal of the surface of the friction elementv hindering volatilization of the binder and reducing so-called bleeding of the binder. In addition, the presence of the nlm on the face of the friction material including the exposed faces of the inlays, prevents excessive liquencation of the softer metal of low melting point at higher working temperatures. Obviously, this prevents loss of the softer metals after repeated cycles of high working temperature. 'I'he inlay, together with the fllm, has an unusually high resistance to wear probably attributable to the fact that plastic or semi-plastic metal is abraded from the element and is redeposited in a new location on the working surfaces.

The coemcient of friction may be varied by changing the type or types of metals in the inlays, for example, the addition or increase of lead or tin to an inlay containing copper lowers the In Figs. 7, 8 and 9, another form is shown wherein 8 indicates the friction element having inlays 9 which extend in staggered relationship from opposite edges of the element. Similarto the forms hereinbefore described, the metal powders are deposited in preformed recesses, as indicated at I0 in Fig. 8; the element being subsequently pressed, cured and, if desired, baked.

Referring particularly to Figs. 10, 11, 12 and 13, our invention is illustrated as applied to a commercial form of clutch facing known to the art as a "Chevron facing. In this type of facing a woven strip is folded longitudinally and wound in spiral fashion in an internested manner, as shown at II in Figs. 10 and 13. In the construction of this type of facing the strip is initially wound relatively loosely whereby the arms I2 of the V-sections are spaced from each other in a divergent manner. The spaces between the adjacent V-sectioned convolutions inherently afford spaces in which powdered metal I3 may be deposited. Preferably the metal is deposited only adjacent one fact of the element, but if relatively high heat conductance is sought, the metal may be deposited adjacent both faces.

The powdered metal may comprise any mixture or combination of metals hereinbefore mentioned and may be deposited or inserted in the facing manually or by means of a hopper (not shown). After the insertion of the metal powders, the facing is compressed at about 5,000 pounds per square inch or higher, cured and baked if necessary, producing anelement` such as that shown at I4 in Figs. 11 and 12. v It will be seen that in the facing I4 a spiral body of metal I5 appears at the surface of the facing interspersed by spiral friction material I6.

If desired, the metal powder may be inserted in the recesses in the elements I, 5 or 8 and between the arms I2 in facing I4 by extrusion. In this case a mixture of 5% bentonite clay, 5% resin and 90% powdered metal may be made into a paste by adding about twice its weight of water and such paste may be extruded into the recesses or interstices. After extruding the facing is dried, pressed, cured and baked in the usual manner. In,such mixtures, the proportions of the selected metal content should be as high as possible consistent with the ability of the mixto flow through the orifice of the extruding head and retain the metal particles in suspension, so that the property of the compressed metallic inlay to smear and form the metallic film heretofore referred to is not appreciably diminished.

Another manner in which the desired association of the powdered metals may be brought about comprises mixing the selected powdered metals and compressing the same into briquets. To accomplish this, the mixed powdered metals are placed in a mold and pressed at 5,000 to 25,000 pounds per square inch or more. In this case the briquets so formed are fitted into slots or recesses preformed in the uncured or semicured friction material which may comprise woven, molded, sheeted or extruded friction material comprising essentially asbestos and a heat hardenable binder. After insertion of the briquets, element is finish cured at full temperature and pressure.

The element is then compressed around the inserted briquet, locking it securely in place.

For most work it is not necessary to sinter the briquet, but where the support or backing of the block is not good, We have foundy it desirablel to slightly sinter the briquet in an inert atmosphere before insertion only to the extent necessary to improve the structural strength ofthe briquet.

'I'he briquets may be formed of any of the mixtures, combinations 4or alloys hereinbefore described and for example the following mixtures are cited; '75% copper, 20% lead, 5% tin, also 62.5 aluminum and 37.5 lead have shown good results. Of course, many other mixtures may be Y used as well as different proportions of the mixtures mentioned and, hence, we do not wish to be limited to these specific examples.

With inserted briquets of this type a metal film is formed as in the other embodiments of our invention previously described and heat dissipation is greatly increased with consequent lower surface temperatures. This latter attribute is inherent also in our hereinbefore described embodiments.

By powdered metal is meant comminuted metal made 4by electro-deposition, oxide reduction or other means. By relatively soft metal of low melting point is meant those metals which are normally rendered plastic at low or moderate operating temperatures, such as lead, tin, antimony, zinc and alloys such as solder, Babbitt type metal or the like. By ductile metals of relatively high melting point is meant those metals which are rendered plastic only at high operating temperatures or which normally are not renderedmaterially plastic at temperatures met within pracy l. A process of making friction elements of the type comprising essentially a fibrous filler and a heat vhardymatble binder, comprising depositinga ypowdered relatively soft metal of low melt-l ing point, anda powderedductile metal of relatively highrnelting point in predetermined portions of the element to form inlays, andv subjecting said element to heat and pressure to densify the inlays andcure and bake the element( 2. Apro'cess of making friction elements of the type comprising essentially a fibrous filler and a heat hardenable binder, comprising depositing powdered metals in predetermined portions of the element to form metal inlays, at least one of said metals comprising a comparatively soft metal of relatively low melting point,v and another comprising a relatively ductile metal of comparatively high melting point, and subjecting said element to heat and pressure to densify the inlays and cure and bake the element.

3. A process of making friction elements of the type comprising essentially a fibrous filler and a heat hardenable binder, comprising depositing powdered metals in predetermined portions of the working face of the element to form metal inlays, at least one of said metals comprising a comparatively soft metal of relatively low melting point and another comprising a relatively ductile metal of comparatively high melting point, and subjecting said element to heat and pressure to densify the inlays and cure and bake the element.

4.. A process o! making friction elements of the type comprising essentially a fibrous ller and a heat hardenable binder, comprising providing recesses in a tace of the element, depositing powdered metals in said recesses to form metal inlays, at least one of said metals scomprising a comparatively soft metal of relatively low` melting point and another comprising a relatively ductile metal of comparatively high melting point, and subjecting said element to heat and pressure to density the inlays and cure and bake the element.

5. In a process wherein a fabric strip carrying a heat hardenable binder is spirally wound to CHRIS BOCmIUS. CLYDE S. BATCHEDOR. JUDSON A. COOK. 

